1. Field of the Invention
The present invention relates to a Cognitive Radio (CR) communication system. More particularly, the present invention relates to a superframe structure, a method and an apparatus for sharing resources between frames when one or more CR systems sharing one channel are overlapped.
2. Description of the Related Art
In an environment where various wireless communication systems are using different spectrums, the lack of available frequencies limits the support of a high-speed multimedia service by allocating a new frequency band. To address the lack of the available frequencies, a Cognitive Radio (CR) technique for raising the frequency utilization is being introduced.
The CR technique allows a Secondary User (SU) to share the band while a Primary User (PU) having the existing frequency license is not using the corresponding band. The CR technique should be able to protect the PUs and to guarantee quality of service of the SUs, which is hereafter referred to as self coexistence. To offer broadband wireless access services over tens of km 100 km, an Institute of Electrical and Electronics Engineers (IEEE) 802.22 Wireless Regional Area Network (WRAN) standardization for sharing the currently allocated TV band based on the CR is under way.
In the CR system having the self coexistence function, a Base Station (BS) scans at least one empty channel not used by the primary/licensed system and establishes the communication over the scanned channel.
When several CR systems are co-located, they need to exchange a Coexistence Beacon Protocol (CBP) packet to increase the spectrum utilization. Meanwhile, when two close CR systems operate the same channel or the neighboring channels, they need to arrange a quiet period for the primary system so as to enhance a channel sensing performance. In the quiet period, they abort the data transmission and scan the channels in use.
To facilitate the self coexistence function, the CR system usually adopts a superframe structure. For example, the IEEE 802.22 standard defines 16 frames in the time axis as one superframe. Herein, the start frame of the superframe is set to deliver a Superframe Control Header (SCH). The standard describes that the structure of the superframe is used in a manner that one CR system or one CR BS occupies all the resources of the superframe unit in one frequency channel. The SCH contains necessary information for the coexistence of not only Customer Premise Equipments (CPEs) in the cell but also the CR systems or the CR BSs.
When the CR system includes a plurality of BSs, the CR systems or the CR BSs have to send the SCH over the same channel because of the small number of the available channels. Since the SCH is transmitted at the start point of the superframe as stated above, when the CR BSs send the SCH at the same time, the transmitted SCHs are likely to collide with each other. That is, when the information for the CPE control and the coexistence of the CR systems (or the CR BSs) is transmitted in the conventional superframe structure, the signal collision between the neighboring CR systems or the neighboring CR BSs can occur.
When the limited channel resources are used, a method and an apparatus are desired for mitigating interference between the BSs, and utilizing and sharing the resources more efficiently. In addition, a superframe structure for the inter-frame information sharing, and a method and an apparatus for efficiently using the limited frequency resources are desired in the CR communication system.